The present invention relates generally to a twist-on wire connector and more particularly to providing an insulator housing which receives a snap-in contoured helical spring. The interior of the housing is contoured to match the contour of the spring.
A typical twist-on wire connector includes an insulated housing of synthetic material having a metallic coil spring insert for receiving twisted, bare wire ends and gripping the wire ends which are forcibly twisted into a threaded engagement with the insert. The coil spring insert is formed by a steel wire having a corrosion resistant plating, e.g. tin, which is coiled into a tapered helical shape and coated with a lubricant which functions as a lubricant for the wire ends as they are twisted into engagement with the coiled insert. The coil insert being tapered, includes a reduced tip end and an enlarged open end. A protruding free end, or kick-out, of the coil is located at the tip end.
The housing also has a tapered configuration including a closed tip end and an enlarged open end. The tip region of the interior annular sidewall of the housing includes flat surfaced reinforcing ribs for mating engagement with the exterior surface of the tip region of the coil insert. The ribs are squared off into a right-angular engagement with the interior of the housing wall. The housing also may include exterior wings adjacent the open end for gripping when the connector and wire ends are being twisted into engagement.
When the coil insert is located in the interior of the housing, an ultrasonic welding tool causes a weld to occur between exterior coil surfaces which engage interior insulator surfaces. It is difficult to weld the kick-out in the solid mass of material in the area of the tip of the housing with consistency. Also, the force exerted by the welding tool deforms the insert to an unknown geometry. The exterior tip region of the coil is welded to the flat surfaces of the ribs during the welding operation.
The twisting engagement of the connector and the bare wire ends during the wire feeding process reveals structural limitations on the wire ends, the coil insert and the housing. When the wire is strand wire, there is clearly a limitation on the amount of torque which can be applied without damage occurring to the strands. Such damage can cause increased resistance across the connection resulting in poor static heating and current cycling. Excessive torque can also distort the wire bundle, the insert and the insulator housing, resulting in a poor electrical connection. The lubricated insert provides insufficient lubrication between the coil and wires. The flat surfaced ribs which engage the tip region of the insert, limit expansion of the coil, inhibit wire feeding to the tip of the insert and concentrate stress at the tip regions of the housing and the coil. In addition, the right-angular engagement between the ribs and the interior of the housing wall may create undesirable stress concentrations.
Excessive torque on the wire bundle can require the wire ends to be re-stripped and joined. As for the insert, excessive torque can further deform the insert within the housing. Excessive torque can also stress the tip region of the housing and cause stress-whitening adjacent the ribs which would result in dielectric failure. Occasionally, a wire end will poke through the housing tip due to excessive torque being applied during wire feeding.
Unfortunately, a suitable solution to the limitations associated with twist on wire connectors related to wire feeding, lubrication, insert distortion and insulator stress has not been satisfactorily addressed by the prior art. Therefore, what is needed is an apparatus for facilitating wire feeding into a twist-on connector. It is also highly desirable to provide a reduced stress environment for the wire and components of the connector.